F21/F25 - Adding a 'forestay' padeye to the deck

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iansan5653
Posts: 101
Joined: Sun May 09, 2021 4:39 pm

F21/F25 - Adding a 'forestay' padeye to the deck

Post by iansan5653 »

I'm working with my sailmaker to design a new jib for my Freedom 21. Originally I was planning to tack the sail to the aft bar of the pulpit so it doesn't interfere with the spinnaker sock outlet. But then I figured why not just continue down past that point to the deck? I could gain another two feet or so of luff length and significantly increase the sail area.

Of course the problem with that idea is that there's nothing on the foredeck at that point to tack the sail to. So I was thinking about installing a big padeye with an oversized backing plate, but I'm still nervous about putting that much load on just the foredeck fiberglass sandwich - I'm scared that when I tension the halyard and load up the mainsheet in heavy air, the padeye will tear a big hole in my foredeck as the mast tries to flex back.

I'm just looking for a little assurance that the deck could handle this load...has anyone done this before? It looks like maybe some Freedom 25s have been rigged like this? How are the larger boats like the F30 and up rigged?

Attached some of the rough drawings we've been working on.
Attachments
top down view
top down view
PXL_20230418_154257714.jpg (1.51 MiB) Viewed 2084 times
side section view
side section view
PXL_20230418_153438345.jpg (1.51 MiB) Viewed 2084 times
Ian Sanders
1983 Freedom 21 - Shoal Draft
St Petersburg (Tampa Bay), FL

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newt2u
Posts: 236
Joined: Wed Sep 11, 2019 11:24 am
Location: UK

Re: F21/F25 - Adding a 'forestay' padeye to the deck

Post by newt2u »

Hi Ian,

I think it is a good idea to add a forestay to your F21. I added one to Rockin over the winter and tested it out a couple of weeks ago. I was able to raise and lower the jib easily and keep it under control so as to swap between the jib and spinnaker without leaving the cockpit. I used 4mm dyneema for mine.

I have no experience with cored decks as Rockin has a solid layup but you should not have any problems if you use a large backplate and reinforce the holes against compression. I used dyneema as it stretches, around 1% at 200Kg, which allows the mast to bend a little. However I question whether you will gain much from that low down area. You are not really getting power from the jib, its main purpose is to turn the air onto the main so that you can point a little higher and there is no main below the pulpit.

btw, I didn't comment in the thread on battens but I love your new mainsail, I am quite jealous. I would love to have a loose foot on my main. I brought back both kicker and outhaul to the cockpit in my mini refit but loosening the outhaul in light winds does nothing to the sail shape and this is when you need it.
Rockin - F21 twin drop keels - located Whitehaven, Cumbria, UK

iansan5653
Posts: 101
Joined: Sun May 09, 2021 4:39 pm

Re: F21/F25 - Adding a 'forestay' padeye to the deck

Post by iansan5653 »

Hmm, that's a good point that the primary purpose is to improve airflow coming into the back of the mainsail. I wonder if the additional area might help with steering balance though? Without the jib I get a lot more weather helm than I'd like.

I'd love to bring the outhaul back to the cockpit. I might have to add that to my todo list now that you mention it.

---

I did some back of the envelope calculations. I guess a 1000 lb load is pretty reasonable to design for, although that is totally arbitrary it 'feels' fair enough for a 21-ft boat. I found a company (https://www.rockwestcomposites.com/shop ... ich-panels) selling foam-core composites and claiming the strength for a 0.75" layup is 139 PSI. I know the fiberglass layers on our deck are much thicker than those panels and balsa core should be stronger than foam-core, so 139 should be a very conservative number. So we need to spread the load over at least roughly 7 sq in. A circle with that area has a radius of 1.5 inches, and I plan to use a much larger backing plate than that. So theoretically at least, I think the deck should be able to handle this easily. Or at least I feel a bit more confident than I did :)
Ian Sanders
1983 Freedom 21 - Shoal Draft
St Petersburg (Tampa Bay), FL

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newt2u
Posts: 236
Joined: Wed Sep 11, 2019 11:24 am
Location: UK

Re: F21/F25 - Adding a 'forestay' padeye to the deck

Post by newt2u »

Even with my tiny self-tacking blade jib, I only get bad weather helm when I should be reefed but it does give me half a knot with a reasonable wind and a few extra degrees into the wind.

I think your estimate is good, conservative even. My dyneema stay will let go at 1500Kg and I do not see that happening in normal sailing. Even in extreme conditions when you have a couple reefs I don't think your load will be anywhere near that. You should probably size your backplate to the breaking load of the line you use.
Rockin - F21 twin drop keels - located Whitehaven, Cumbria, UK

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